1. Field of the Invention
The present invention relates to a gas turbine seal apparatus for preventing cooling air from leaking into a high temperature combustion gas passage between an end portion of a moving blade platform and a stationary blade inside shroud.
2. Description of the Related Art
FIG. 4 is a cross sectional view which shows a seal apparatus for preventing cooling air from leaking between a moving blade and a stationary blade of a conventional gas turbine. In the drawing, reference numeral 1 denotes a moving blade, reference numeral 2 denotes a platform thereof, and reference numeral 3 denotes a seal pin inserted between the adjacent platforms in a circumferential direction and constituted by a seal pin 3a extending in an axial direction and a seal pins 3b provided on both sides in an inclined manner. Reference numeral 4 denotes a shank portion disposed below the platform 2, reference numeral 5 denotes a disc, and reference numerals 6 and 7 denote seal plates for sealing opposite sides of the shank portion 4.
Reference numeral 11 denotes a stationary blade, reference numeral 12 denotes an inside shroud, and reference numeral 13 denotes an outside shroud. Reference numeral 14 denotes a cavity disposed below the inside shroud 12, reference numeral 15 denotes a seal box, and reference numerals 16 and 17 denote honeycomb seals mounted on front and rear end portions 12a, 12b of the inside shroud 12. The honeycomb seals 16, 17 are structured such that a plurality of honeycomb cores are disposed in such a manner as to be open downward. Reference numerals 18 and 19 each denote a space formed by the seal plates 6 and 7 of the moving blade 1 and the adjacent stationary blade 11, and these spaces are areas where high air pressure is formed.
In the structure of the moving blade and the stationary blade mentioned above, cooling air is introduced to the moving blade 1 from the disc 5 through a passage (not shown) by suppling the cooling air from the shank portion 4 to a cooling passage for the moving blade 1. However, the cooling air leaks from a contact portion between the seal pins 3a and 3b or a gap between the platforms adjacent to the end portions 2a and 2b of the platform 2, and the air directly flows out to the spaces 18 and 19 or the combustion gas passage. Further, since air for the stationary blade 11 leaks from the cavity 14 through the seal box 15, the spaces 18 and 19 are under high pressure. The end portions 2a and 2b of the platform 2 in the moving blade 1 and the honeycomb seals 17 and 16 provided on the inside shroud 12 of the stationary blade 11 are opposed to each other so as to form the seal mechanisms. The seal mechanisms are intended to prevent more than the necessary amount of cooling air from leaking into the high temperature combustion gas passage and being wasted.
As mentioned above, the seal between the moving blade platform and the stationary blade inside shroud end portion in the conventional gas turbine is constructed as shown in FIG. 4 such that the seals are formed between the honeycomb seals 16 and 17 provided on both ends 12a and 12b of the inside shroud 17 in the stationary blade 11 and the end portions 2b and 2a of the moving blade platform 2. Thereby sealing the air which is going to escape into the high temperature combustion gas passage. However, in this seal mechanism, the end portions 2a and 2b of the platform 2 have a simple shape in comparison with the honeycomb seals 17 and 18, and thus the sealing performance is not always good, so that the seal is insufficient. Accordingly, more than the necessary amount of the sealing air tends to leak into the high temperature combustion gas passage, so that the amount of cooling air is increased, thereby inviting deterioration in the performance of the gas turbine.
In the seal mechanisms, as the flow passage becomes complex and the resistance is increased, the leakage of air is reduced and the sealing performance is improved. However, in the honeycomb seals 16 and 17, the air goes in and out through an inner portion of a multiplicity of honeycomb cores, and the flow becomes complex and the resistance to the flow is increased so as to provide a sealing effect. In contrast, the end portions 2a and 2b of the platform 2 have a simple shape so that the effect of the flow resistance is not adequately obtained. Accordingly, there is room for improving the current seal mechanism.